Conventional catheter ablation procedures in electrophysiology (EP) can be guided by x-ray fluoroscopy, often complemented by an electromagnetic tracking (EMT) system for tracking a catheter. For the guidance by x-ray fluoroscopy an x-ray fluoroscopy system is used, which acquires x-ray projection images during the catheter ablation procedure. The x-ray projection images can be registered with a pre-operative three-dimensional image like a computed tomography (CT) or magnetic resonance (MR) image, in order to provide three-dimensional anatomical information during the catheter ablation procedure. In particular, the position of the catheter tracked by the EMT system may be shown within the pre-operative three-dimensional image, in order to show the position of the catheter relative to an inner three-dimensional anatomy of a patient. However, acquiring the x-ray projection images leads to a relatively high radiation dose applied to the patient.